1. Field of the Invention
The present invention relates to a toner for use in an electrophotographic method, an electrostatic recording method, an electrostatic printing method, a toner jet recording method and a magnetic recording method.
2. Related Background Art
As electrophotography color image forming apparatus have become widely used, the application purposes thereof are extended variously, creating a severe demand on image quality. When copying images such as common photographs, catalogs and maps, even fine details are demanded to be finely and faithfully reproduced, and accordingly demand for vividness of color is also growing and the color reproduction range is demanded to be extended. In particular, under the current circumstances such that electrophotography has been significantly adopted in the field of printing, electrophotography itself is demanded to have high definition, high fineness, graininess and the like equal to or higher than those involved in the printing quality.
Full color image copying machines having been proposed in these years generally adopt a method in which a plurality of photosensitive members are used, electrostatic charge images formed on the photosensitive members are developed respectively by use of a cyan toner, a magenta toner, a yellow toner and a black toner, thereafter the toner images are successively transferred onto a transfer material conveyed along a straight path between the photosensitive members and a belt-form transfer member to form a full-color image, or a method in which a transfer material is wound, with the aid of electrostatic force or a mechanical action exerted by grippers, around the surface of a transfer member which faces a photosensitive member, and a development-transfer cycle is repeated four times to form a full-color image.
Toners used in such full-color image copying machines are required to exhibit an improved color reproducibility and to permit a sufficient color mixing of the respective toners in a heat-pressure fixing to ensure satisfactory transparency for overhead projector (OHP) images to be heat fixed onto transfer materials. In order to satisfy such requirements, a resin having a sharper melting property is preferably used, in this connection polyester resin having been used recently as a sharp-melting resin. As polymerization catalysts for producing polyester resins for use in toners, tin based catalysts such as dibutyltin oxide and antimony based catalysts such as antimony trioxide have been generally used. In order to realize performances required for full-color image copying machines such as high speed, high image quality and high fineness, important are such toner properties as fixing property including low temperature fixing property and high-temperature offset resistance, and color reproducibility including color mixability and transparency; however, polyester resins obtained by use of catalysts such as described above are still far from satisfying these toner properties.
Accordingly, Japanese Patent Applications Laid-Open Nos. 2002-148867 and 2001-64378 propose techniques in which a titanic acid ester of an aromatic diol and a solid titanium compound are used as polymerization catalysts. Japanese Patent Application Laid-Open No. H05-279465 proposes a technique in which a titanium tetraalkoxide treated with an organic monocarboxylic acid is used as a polycondensation catalyst for a polyester resin. However, these techniques still have problems with fixing property, color reproducibility and developing property when applied to toners for full-color image formation, and are therefore needed to be further improved.
When a sharp melting resin is used, a problem with high-temperature offset resistance usually tends to occur at the time of melting of the toner in the heat-pressure fixing step because the binder resin is low in self-cohesion. Accordingly, for the purpose of improving the high-temperature offset resistance at the time of fixing, relatively high-crystallinity waxes typified by polyethylene wax and polypropylene wax are used as releasing agents. However, because of the high crystallinity of the mold releasing agent and the difference in refractive index between the mold releasing agent and the OHP sheet material, such toners for full-color image formation sometimes lead to the degradation of transparency and the lowering of the chroma and brightness in the projected images when OHP projection is carried out.
For the purpose of solving these problems, Japanese Patent Applications Laid-Open Nos. H04-149559 and H04-107467 propose methods in which a nucleating agent is used together with a wax to lower the crystallinity of the wax. Japanese Patent Applications Laid-Open Nos. H04-301853 and H05-61238 propose methods in which a wax further lower in crystallinity is used (for example, see Patent Documents 6 and 7). Japanese Patent Applications Laid-Open Nos. H01-185660 and H01-238672 also propose the use of montan waxes as waxes, other than those described above, each having a relatively good transparency and a low melting point. However, such waxes cannot fully satisfy all the requirements, namely, the toner transparency in OHP sheets, and low-temperature fixing property and high-temperature offset resistance in the heat-pressure fixing.